如何确定对象是否实现了特定方法？

I am iterating through an NSArray that contains many different types of objects. There are many methods to figure out what class the object is. However, I haven't been able to find a good way to find out if an object can implement a particular function. I can put it in a try-catch but it will still output an error message in the console even if I'm catching the error. Is there a better way to do this?

我正在迭代包含许多不同类型对象的NSArray。有很多方法可以确定对象是什么类。但是,我无法找到一个好方法来确定对象是否可以实现特定的功能。我可以把它放在try-catch中,但即使我正在捕获错误,它仍会在控制台中输出错误消息。有一个更好的方法吗?

Simple example:

@try {
    if ([element lowercaseString]) {
        //do something
    }
}
@catch (id theException) {
    // do something else
}

3 个解决方案

#1

As suggested, you can use respondsToSelector: message declared on NSObject. The provided code would be like

如建议的那样,您可以使用在NSObject上声明的respondsToSelector:消息。提供的代码就像

if ([element respondsToSelector:@selector(lowercaseString)]) {
    // ... do work
}

#2

Look at NSObject's respondsToSelector method

查看NSObject的respondsToSelector方法

#3

A nice generic category to have in your code is this:

您的代码中有一个很好的通用类别:

@interface NSObject (KMExtensions)

- (id)performSelectorIfResponds:(SEL)aSelector;
- (id)performSelectorIfResponds:(SEL)aSelector withObject:(id)anObject;

@end

@implementation NSObject (KMExtensions)

- (id)performSelectorIfResponds:(SEL)aSelector
{
    if ( [self respondsToSelector:aSelector] ) {
        return [self performSelector:aSelector];
    }
    return NULL;
}

- (id)performSelectorIfResponds:(SEL)aSelector withObject:(id)anObject
{
    if ( [self respondsToSelector:aSelector] ) {
        return [self performSelector:aSelector withObject:anObject];
    }
    return NULL;
}

@end

And then you can use:

然后你可以使用:

[element performSelectorIfResponds:@selector(lowercaseString)];

#1